Solar cell and method for manufacturing the same

ABSTRACT

Disclosed is a solar cell including a first electrode, a second electrode, and a first conversion layer disposed therebetween. The first electrode is closer to a light incident side than the second electrode. The first conversion layer is a composition-gradient perovskite. A part of the first conversion layer adjacent to the first electrode has an energy gap less than that of a part of the first conversion layer adjacent to the second electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.14/584,908 (now U.S. Pat. No. 9,349,967), filed on Dec. 29, 2014 andentitled “Solar cell and method for manufacturing the same”, which isbased on, and claims priority from, Taiwan Application Serial Number103143429, filed on Dec. 12, 2014, and claims the benefit of U.S.Provisional Application No. 62/025,180, filed on Jul. 16, 2014, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The technical field relates to a perovskite conversion layer of a solarcell, and in particular it relates to a composition-gradient perovskitelayer and method for manufacturing the same.

BACKGROUND

Organic metal perovskite materials are potential materials for solarcells due to their excellent physical properties. Organic lead halideperovskite has a higher efficiency over other perovskite materials. Themajor conventional method for forming a perovskite layer is coating. Forexample, two precursors of the perovskite are dissolved in an organicsolvent (e.g. DMF), and then spin-coated on an electrode. Alternatively,lead halide (PbX₂) can be dissolved in an organic solvent andspin-coated to form a PbX₂ film on an electrode, and the PbX₂ film isthen dipped in methylammonium iodide (MAI) to form a perovskite film ofPb(CH₃NH₃)X₂I. However, the solvent in the next coating step maydissolve the previously formed perovskite film formed previously. Evenif the compositions in each of the coating processes are different, thesolvent in different coating processes may dissolve the differentcompositions in previous coating processes. In short, the generalcoating processes cannot form a composition-gradient perovskite layer.

Accordingly, a novel method for manufacturing a composition-gradientperovskite layer is called-for.

SUMMARY

One embodiment of the disclosure provides a method of manufacturing asolar cell, comprising: providing m parts by mole of M¹X¹ ₂ by a firstdeposition source, providing 1−m parts by mole of M²X² ₂ by a seconddeposition source, and providing an amount of AX¹ _(t)X² _((1−t)) by athird deposition source to deposit a first conversion layer on a firstelectrode, wherein the first conversion layer is a composition-gradientperovskite; and forming a second electrode on the first conversionlayer, wherein a part of the first conversion layer adjacent to thefirst electrode has an energy gap lower than that of a part of the firstconversion layer adjacent to the second electrode, wherein the firstconversion layer has a composition of M¹ _(m)M² _((1−m))AX¹ _((2m+t))X²_((3−2m−t)), m is decreased with a longer deposition time, t isdecreased with a longer deposition time, 1≧m≧0, and 1≧t≧0; wherein eachof M¹ and M² is independently a divalent cation of Ge, Sn, or Pb,wherein A is a monovalent cation of methylammonium, ethylammonium, orformamidinium, wherein each of X¹ and X² is independently a monovalentanion of halogen, wherein M¹ has a lower atomic number than M², X¹ has ahigher atomic number than X², or a combination thereof.

One embodiment of the disclosure provides a method of manufacturing asolar cell, comprising: providing m parts by mole of M¹X¹ ₂ by a firstdeposition source and providing 1−m parts by mole of M²X² ₂ by a seconddeposition source to deposit a M¹ _(m)M² _((1−m))X¹ _(2m)X² _((2−2m))layer on a first electrode; providing AX¹ or AX² by a third depositionsource, such that AX¹ or AX² reacts with the M¹ _(m)M² _((1−m))X¹_(2m)X² _((2−2m)) layer to form a first conversion layer on the firstelectrode, wherein the first conversion layer is a composition-gradientperovskite of M¹ _(m)M² _((1−m))AX¹ _((2m+1))X² _((2−2m)) or M¹ _(m)M²_((1−m))AX¹ _((2m))X² _((3−2m)); and forming a second electrode on thefirst conversion layer, wherein a part of the first conversion layeradjacent to the first electrode has an energy gap lower than that of apart of the first conversion layer adjacent to the second electrode,wherein m is decreased with a longer deposition time and 1≧m≧0; whereineach of M¹ and M² is independently a divalent cation of Ge, Sn, or Pb,wherein A is a monovalent cation of methylammonium, ethylammonium, orformamidinium, wherein each of X¹ and X² is independently a monovalentanion of halogen, wherein M¹ has a lower atomic number than M², X¹ has ahigher atomic number than X², or a combination thereof.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows the deposition of the conversion layer in one embodiment ofthe disclosure;

FIGS. 2A and 2B show lines of concentration versus deposition time ofM¹X¹ ₂, M²X² ₂, and AX¹ _(t)X² _((1−t)) in the deposition chamber ofembodiments in the disclosure;

FIG. 3 shows a solar cell in one embodiment of the disclosure;

FIGS. 4A, 4B, 4C, 4D, and 4E show lines of energy gap versus thicknessof conversion layers in embodiments of the disclosure;

FIG. 5 shows a solar cell in one embodiment of the disclosure;

FIG. 6 shows the deposition of the conversion layer in one embodiment ofthe disclosure;

FIGS. 7A and 7B show lines of energy gap versus thickness of conversionlayers in embodiments of the disclosure; and

FIGS. 8A, 8B, and 8C show lines of energy gap versus thickness ofconversion layers in embodiments of the disclosure.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare shown schematically in order to simplify the drawing.

One embodiment of the disclosure provides a method for manufacturing asolar cell. As shown in FIG. 1, m parts by mole of M¹X¹ ₂ is provided bya deposition source 11, 1−m parts by mole of M²X² ₂ is provided by adeposition source 13, and an amount of AX¹ _(t)X² _((1−t)) is providedby a deposition source 15, thereby depositing a conversion layer 17 on afirst electrode 19, wherein the conversion layer is acomposition-gradient perovskite. FIGS. 2A and 2B show concentrations ofM¹X¹ ₂, M²X² ₂, and AX¹ _(t)X² _((1−t)) at different deposition times inthe deposition chamber of embodiments in the disclosure. Note thatalthough only 1 part by mole of M¹X¹ ₂ reacts with AX¹ to form M¹AX¹ ₃at start in FIGS. 2A and 2B, M¹X¹ ₂, M²X² ₂, and AX¹ _(t)X² _((1−t)) mayreact to form M¹ _(m)M² _((1−m))AX¹ _(2m+t)X² _(3−2m−t) at the start. Inshort, deposition can be started at time point T in FIGS. 2A and 2Brather than at time point 0. While the deposition time is increased, them and t are decreased, 1≧m≧0, and 1≧t≧0. M¹ _(m)M² _((1−m))AX¹ _(2m+t)X²_(3−2m−t) can be represented as M¹ _(m)M² _((1−m))A[X¹ _(x)X²_((1−x))]₃, wherein x=(2m+t)/3, and m and x are greater at a locationthat is closer to the electrode 19. Each of M¹ and M² is independently adivalent cation of Ge, Sn, or Pb. A is a monovalent cation ofmethylammonium, ethylammonium, or formamidinium. Each of X¹ and X² isindependently a monovalent anion of halogen. M¹ has a lower atomicnumber than M², X¹ has a higher atomic number than X², or a combinationthereof.

Subsequently, an electrode 31 can be formed on the conversion layer 17,as shown in FIG. 3. In one embodiment, the electrode 19 is an electrodeof a light-incident side, and its composition should be transparent andelectrically conductive such as fluorine doped tin oxide (FTO), indiumtin oxide (ITO), zinc tin oxide (ZTO), or the like. The electrode 31 canbe a general electrical conductor such as carbon material (e.g. activecarbon or graphene) or metal (e.g. gold, silver, copper, aluminum,another electrically conductive metal, or an alloy thereof). In oneembodiment, a metal oxide semiconductor material (e.g. titanium oxide,zinc oxide, nickel oxide, or tungsten oxide) can be disposed between theelectrode 19 and the conversion layer 17 to serve as an electrontransport layer. In another embodiment of the disclosure, a holetransport material such as Spiro-OMeTAD, P3HT, CuSCN, CuI, or PEDOT:PSScan be disposed between the electrode 31 and the conversion layer 17 toserve as a hole transport layer.

The composition-gradient conversion layer 17 formed in FIG. 2A has anenergy gap diagram as shown in FIG. 4A, and the composition-gradientconversion layer 17 has an energy gap diagram as shown in FIG. 4B. Itshould be understood that the composition-gradient conversion layer 17,with a part adjacent to the electrode 19 having an energy gap lower thanthat of a part adjacent to the electrode 31, can be formed by the aboveprocesses. In addition, the energy gap of the conversion layer 17 mayhave other designs as shown in FIG. 4C, 4D, or 4E.

In one embodiment, the M¹X¹ ₂ provided by the deposition source 11 inFIG. 1 is SnI₂, the M²X² ₂ provided by the deposition source 13 in FIG.1 is PbI₂, and the AX¹ _(t)X² _((1−t)) provided by the deposition source15 was (CH₃NH₃)I. As such, a part of the conversion layer 17 adjacent tothe electrode 19 can be Sn(CH₃NH₃)I₃ with an energy gap of 1.1 eV, apart of the conversion layer 17 adjacent to the electrode 31 can bePb(CH₃NH₃)I₃ with an energy gap of 1.5 eV, and the composition betweenthe electrodes 19 and 31 can be Sn_(m)Pb_((1−m))(CH₃NH₃)I₃.

In one embodiment, the M¹X¹ ₂ provided by the deposition source 11 inFIG. 1 is PbI₂, the M²X² ₂ provided by the deposition source 13 in FIG.1 is PbBr₂, and the AX¹ _(t)X² _((1−t)) provided by the depositionsource 15 was (CH₃NH₃)I_(t)Br_((1−t)). As such, a part of the conversionlayer 17 adjacent to the electrode 19 can be Pb(CH₃NH₃)I₃ with an energygap of 1.5 eV, a part of the conversion layer 17 adjacent to theelectrode 31 can be Pb(CH₃NH₃)Br₃ with an energy gap of 2.3 eV, and thecomposition between the electrodes 19 and 31 can bePb(CH₃NH₃)[I_(x)Br_((1−x))]₃.

The deposition sources 11, 13, and 15 can be sputtering sources orevaporation sources. If the sputtering sources are selected, the ratioof M¹X¹ ₂ and M²X² ₂ can be fine-tuned by controlling the energybombarding the target. If the evaporation sources are selected, theratio of M¹X¹ ₂ and M²X² ₂ can be fine-tuned by controlling thetemperature of the evaporation sources. In addition, the ratio of X¹ andX² in AX¹ _(t)X² _((1−t)) can be fine-tuned by controlling the flow rateof the halogen gas reacting with A.

In another embodiment of the disclosure, a conversion layer 18 can bedeposited on the electrode 19 before depositing the conversion layer 17on the electrode 19. As shown in FIG. 5, the conversion layer 18 isdisposed between the electrode 19 and the conversion layer 17. A part ofthe conversion layer 18 adjacent to the electrode 19 has an energy gaphigher than that of a part of the conversion layer 18 adjacent to theconversion layer 17, a part of the conversion layer 18 adjacent to theconversion layer 17 has an energy gap equal to that of a part of theconversion layer 17 adjacent to the conversion layer 18, and a part ofthe conversion layer 18 adjacent to the electrode 19 has an energy gaplower than that of a part of the conversion layer 17 adjacent to theelectrode 31.

In one embodiment, the step of depositing the conversion layer 18 isdescribed as below. m′ parts by mole of M³X³ ₂ is provided by adeposition source 61, 1−m′ parts by mole of M⁴X⁴ ₂ is provided by adeposition source 63, and an amount of AX³ _(t′)X⁴ _((1−t′)) is providedby a deposition source 65 to deposit the conversion layer 18 on theelectrode 19, as shown in FIG. 6. The conversion layer 18 has acomposition of M³ _(m′)M⁴ _((1−m′))AX³ _((2m′+t′))X⁴ _((3−2m′−t′)), m isdecreased with a longer deposition time, t is decreased with a longerdeposition time, 1≧m′≧0, and 1≧t′≧0. M³ _(m′)M⁴ _((1−m′))AX³_((2m′+t′))X⁴ _((3−2m′−t′)) can be represented as M³ _(m′)M⁴_((1−m′))A[X³ _(x′)X_((1−x′)) ⁴]₃, wherein x′=(2m′+t′)/3, and m′ and x′are greater at a location that is closer to the electrode 19. Each of M³and M⁴ is independently a divalent cation of Ge, Sn, or Pb, A is amonovalent cation of methylammonium, ethylammonium, or formamidinium,and each of X³ and X⁴ is independently a monovalent anion of halogen. M³has a higher atomic number than M⁴, X³ has a lower atomic number thanX⁴, or a combination thereof.

The deposition sources 61, 63, and 65 can be sputtering sources orevaporation sources. If the sputtering sources are selected, the ratioof M³X³ ₂ and M⁴X⁴ ₂ can be fine-fine-tuned by controlling the energybombarding the target. If the evaporation sources are selected, theratio of M³X³ ₂ and M⁴X⁴ ₂ can be fine-tuned by controlling thetemperature of the evaporation sources. In addition, the ratio of X³ andX⁴ in AX³ _(t)X⁴ _((1−t)) can be fine-tuned by controlling the flow rateof the halogen gas reacting with A.

In one embodiment of the disclosure, the composition of a part of theconversion layer 18 adjacent the electrode 19 is gradually changed fromPb(CH₃NH₃)[I_(x)Br_((1−x))]₃ (0<x<1) to Pb(CH₃NH₃)I₃, and thecomposition of the conversion layer 17 is gradually changed fromPb(CH₃NH₃)I₃ (the interface between the conversion layers 17 and 18) toPb(CH₃NH₃)Br₃. In another embodiment, the composition of a part of theconversion layer 18 adjacent the electrode 19 is gradually changed fromSn_(m)Pb_((1−m))(CH₃NH₃)I₃ (0<m<1) to Sn(CH₃NH₃)I₃, and the compositionof the conversion layer 17 is gradually changed from Sn(CH₃NH₃)I₃ (theinterface between the conversion layers 17 and 18) to Pb(CH₃NH₃)I₃.

For example, the conversion layers 18 and 17 may have energy gapdiagrams as shown in FIG. 7A or 7B. Note that the energy gap diagram ofthe conversion layers 18 and 17 can be fine-tuned with other changes inFIGS. 4B to 4E.

In another embodiment, m parts by mole of M¹X¹ ₂ is provided by adeposition source 11 and 1−m parts by mole of M²X² ₂ is provided by adeposition source 13 to deposit a M¹ _(m)M² _((1−m))X¹ _(2m)X² _((2−2m))layer on an electrode 19. Thereafter, AX¹ or AX² is provided by adeposition source 15, such that AX¹ or AX² reacts with the M¹ _(m)M²_((1−m))X¹ _(2m)X² _((2−2m)) layer to form a conversion layer 17 on theelectrode 19, wherein the conversion layer 17 is a composition-gradientperovskite of M¹ _(m)M² _((1−m))AX¹ _((2m+1))X² _((2−2m)) or M¹ _(m)M²_((1−m))AX¹ _((2m))X² _((3−2m)). An electrode 31 is then formed on theconversion layer 17, as shown in FIG. 3. M¹ _(m)M² _((1−m))AX¹_((2m+1))X² _((2−2m)) can be represented as M¹ _(m)M² _((1−m))A[X_(x)X²_((1−x))]₃, wherein x=(2m+1)/3, and m and x are greater at a locationthat is closer to the electrode 19. M¹ _(m)M² _((1−m))AX¹ _((2m))X²_((3−2m)) can be represented as M¹ _(m)M² _((1−m))A[X¹ _(x)X²_((1−x))]₃, wherein x=2m/3, and m and x are greater at a location thatis closer to the electrode 19.

A part of the conversion layer 17 adjacent to the electrode 19 has anenergy gap lower than that of a part of the conversion layer 17 adjacentto the electrode 31. In the above deposition, m is decreased with alonger deposition time and 1≧m≧0. Each of M¹ and M² is independently adivalent cation of Ge, Sn, or Pb. A is a monovalent cation ofmethylammonium, ethylammonium, or formamidinium. Each of X¹ and X² isindependently a monovalent anion of halogen. In the composition of theconversion layer 17, M¹ has a lower atomic number than M², X¹ has ahigher atomic number than X², or a combination thereof.

Compared to above embodiments, this embodiment is different due to theM¹ _(m)M² _((1−m))X¹ _(2m)X² _((2−2m)) is pre-formed and AX¹ or AX² arethen provided to react with M¹ _(m)M² _((1−m))X¹ _(2m)X² _((2−2m)) toform the conversion layer, rather than the M¹X¹, M²X², and AX¹ (or AX²)are simultaneously provided and reacted to directly from the conversionlayer. The composition and the energy gap diagram of the conversionlayer 17 in this embodiment are similar to that in the above embodimentsand omitted here.

Similar to the above embodiments, a composition-gradient conversionlayer 18 can be further deposited on the electrode 19 before depositingthe conversion layer 17 in this embodiment. In other words, theconversion layer 18 is disposed between the conversion layer 17 and theelectrode 19. A part of the conversion layer 18 adjacent to theelectrode 19 has an energy gap higher than that of a part of theconversion layer 18 adjacent to the conversion layer 17, a part of theconversion layer 18 adjacent to the conversion layer 17 has an energygap equal to that of a part of the conversion layer 17 adjacent to theconversion layer 18, and a part of the conversion layer 18 adjacent tothe electrode 19 has an energy gap lower than that of a part of theconversion layer 17 adjacent to the electrode 31. For example, theenergy gap of the conversion layers 18 and 17 can be referred to FIGS.7A and 7B.

In one embodiment, the step of depositing the conversion layer isdescribed as below. m′ parts by mole of M³X³ ₂ is provided by thedeposition source 61 and 1−m′ parts by mole of M⁴X⁴ ₂ is provided by thedeposition source 63 to deposit a M³ _(m′)M⁴ _((1−m′))X³ _(2m′)X⁴_((2−2m′)) layer on the electrode 19. AX³ or AX⁴ is then provided by thedeposition source 65, such that AX³ or AX⁴ reacts with the M³ _(m′)M⁴_((1−m′))X³ _(2m′)X⁴ _((2−2m′)) layer to form a conversion layer 18 onthe electrode 19, wherein the conversion layer 18 is acomposition-gradient perovskite of M³ _(m′)M⁴ _((1−m′))AX³ _((2m′+1))X⁴_((2−2m′)) or M³ _(m′)M⁴ _((1−m′))AX³ _((2m′))X⁴ _((3−2m′)). M³ _(m′)M⁴_((1−m′))AX³ _((2m′+1))X⁴ _((2−2m′)) can be represented as M³ _(m′)M⁴_((1−m′))A[X³ _(x′)X⁴ _((1−x′))]₃, wherein x′=(2m′+1)/3, and m′ and x′are greater at a location that is closer to the electrode 19. M³ _(m′)M⁴_((1−m))AX³ _((2m′))X⁴ _((3−2m′)) can be represented as M³ _(m′)M⁴_((1−m′))A[X³ _(x′)X⁴ _((1−x′))]₃, wherein x′=(2m′)/3, and m′ and x′ aregreater at a location that is closer to the electrode 19. m′ isdecreased with a longer deposition time and 1≧m′≧0. Each of M³ and M⁴ isindependently a divalent cation of Ge, Sn, or Pb, A is a monovalentcation of methylammonium, ethylammonium, or formamidinium, and each ofX³ and X⁴ is independently a monovalent anion of halogen. In thecomposition of the conversion layer 18, M³ has a higher atomic numberthan M⁴, X³ has a lower atomic number than X⁴, or a combination thereof.

Compared to conventional skills, the processes of manufacturing theperovskite conversion layers in the disclosure are free of solvent. Assuch, the different perovskite compositions in different layers will notbe dissolved and mixed by solvent. In other words, the method of thedisclosure may control the perovskite composition in differentthicknesses of the conversion layer, thereby tuning the energy gap ofthe conversion layer to improve the conversion efficiency of the solarcell.

Below, exemplary embodiments will be described in detail with referenceto the accompanying drawings so as to be easily realized by a personhaving ordinary knowledge in the art. The inventive concept may beembodied in various forms without being limited to the exemplaryembodiments set forth herein. Descriptions of well-known parts areomitted for clarity, and like reference numerals refer to like elementsthroughout.

EXAMPLES Comparative Example 1

In FIG. 3, the electrode 19 was a TiO₂ layer with a thickness of 90 nm,the electrode 31 was a thin gold film, the conversion layer 17 was aPb(CH₃NH₃)I₃ layer with a thickness of 400 nm, and a hole transportlayer (not shown) between the conversion layer 17 and the electrode 31was a Spiro-OMeTAD layer with a thickness of 400 nm. The properties ofthe above solar cell were simulated and calculated by Analysis ofMicroelectronic and Photonic Structures-1D (AMPS-1D) as described below.The solar cell had an open-circuit voltage of 1.272V, a short-circuitcurrent of 21.683 mA/cm², a filling factor of 0.826, and a conversionefficiency of 22.722%.

Comparative Example 2

In FIG. 3, the electrode 19 was a TiO₂ layer with a thickness of 90 nm,the electrode 31 was a thin gold film, and the conversion layer 17 was aPb(CH₃NH₃)I₃ layer with a thickness of 400 nm. The properties of theabove solar cell were simulated and calculated by AMPS-1D as describedbelow. The solar cell had an open-circuit voltage of 0.838V, ashort-circuit current of 17.945 mA/cm², a filling factor of 0.804, and aconversion efficiency of 12.095%.

Example 1

In FIG. 3, the electrode 19 was a TiO₂ layer with a thickness of 90 nm,the electrode 31 was a thin gold film, a part of the conversion layer 17adjacent to the electrode 19 was Pb(CH₃NH₃)I₃ with a thickness of 300nm, and a composition-gradient part of the conversion layer 17 wasPb(CH₃NH₃)[I_(x)Br_((1−x))]₃ with a thickness of 100 nm extending fromPb(CH₃NH₃)I₃ to Pb(CH₃NH₃)Br₃. The conversion layer 17 had an energy gapdiagram as shown in FIG. 8A. The properties of the above solar cell weresimulated and calculated by AMPS-1D as described below. The solar cellhad an open-circuit voltage of 1.284V, a short-circuit current of 21.136mA/cm², a filling factor of 0.840, and a conversion efficiency of22.807%.

Example 2

In FIG. 3, the electrode 19 was a TiO₂ layer with a thickness of 90 nm,the electrode 31 was a thin gold film, and the conversion layer 17 wasdivided to three regions from the electrode 19 to the electrode 31: (1)a composition-gradient part of Pb(CH₃NH₃)[I_(x)Br_((1−x))]₃ with athickness of about 50 nm gradually changed to Pb(CH₃NH₃)I₃, wherein thePb(CH₃NH₃)[I_(x)Br_((1−x))]₃ had an energy gap that gradually changedfrom 1.5 eV (or 1.6 eV, 1.8 eV, 2.0 eV, 2.3 eV) to 1.5 eV; (2) a part ofPb(CH₃NH₃)I with a thickness of about 300 nm, wherein the Pb(CH₃NH₃)Ihad an energy gap of 1.5 eV; and (3) a composition-gradient part ofPb(CH₃NH₃)[I_(x)Br_((1−x))]₃ with a thickness of about 50 nm graduallychanged to Pb(CH₃NH₃)Br₃, wherein the Pb(CH₃NH₃)[I_(x)Br_((1−x))]₃ hadan energy gap that gradually changed from 1.5 eV to 2.3 eV. Theconversion layer 17 had an energy gap diagram as shown in FIG. 8B. Theproperties of the above solar cells, e.g. an open-circuit voltage, ashort-circuit current, a filling factor, and a conversion efficiency,were simulated and calculated by AMPS-1D and tabulated in Table 1.

TABLE 1 The energy gap of the part of the conversion Open- Short-Conver- layer 17 adjacent to circuit circuit Fill- sion the electrode 19voltage current ing efficiency (Eg) (V) (mA/cm²) factor (%) 1.5 1.27821.448 0.839 23 1.6 1.283 21.393 0.84 23.051 1.8 1.284 21.217 0.83922.863 2.0 1.289 21.187 0.673 18.399 2.3 1.566 21.162 0.256 8.439

Example 3

In FIG. 3, the electrode 19 was a TiO₂ layer with a thickness of 90 nm,the electrode 31 was a thin gold film, and the conversion layer 17 wasdivided to three regions from the electrode 19 to the electrode 31: (1)a composition-gradient part of Pb(CH₃NH₃)[I_(x)Br_((1−x))]₃ with athickness of about 50 nm (or 100 nm, 200 nm, 300 nm, 350 nm) graduallychanged to Pb(CH₃NH₃)I₃, wherein the Pb(CH₃NH₃)[I_(x)Br_((1−x))]₃ had anenergy gap that gradually changed from 1.6 eV to 1.5 eV; (2) a part ofPb(CH₃NH₃)I with a thickness of about 300 nm (or 250 nm, 150 nm, 50 nm,0 nm), wherein the Pb(CH₃NH₃)I had an energy gap of 1.5 eV; and (3) acomposition-gradient part of Pb(CH₃NH₃)[I_(x)Br_((1−x))]₃ with athickness of about 50 nm gradually changed to Pb(CH₃NH₃)Br₃, wherein thePb(CH₃NH₃)[I_(x)Br_((1−x))]₃ had an energy gap that gradually changedfrom 1.5 eV to 2.3 eV. The conversion layer 17 had an energy gap diagramas shown in FIG. 8C. The properties of the above solar cells, e.g. anopen-circuit voltage, a short-circuit current, a filling factor, and aconversion efficiency, were simulated and calculated by AMPS-1D andtabulated in Table 2.

TABLE 2 The thickness The thickness of region of region (1) of the (2)of the Open- Short- Conver- conversion conversion circuit circuit Fill-sion layer 17 layer 17 voltage current ing efficiency (nm) (nm) (V)(mA/cm²) factor (%) 50 300 1.283 21.393 0.84 23.051 100 250 1.289 21.3360.84 23.113 200 150 1.304 21.222 0.841 23.289 300 50 1.327 21.101 0.84223.582 350 0 1.344 21.034 0.843 23.830

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed methods andmaterials. It is intended that the specification and examples beconsidered as exemplary only, with a true scope of the disclosure beingindicated by the following claims and their equivalents.

What is claimed is:
 1. A method of manufacturing a solar cell,comprising: providing m parts by mole of M¹X¹ ₂ by a first depositionsource, providing 1-m parts by mole of M²X² ₂ by a second depositionsource, and providing an amount of AX¹ _(t)X² _((1−t)) by a thirddeposition source to deposit a first conversion layer on a firstelectrode; and forming a second electrode on the first conversion layer,wherein a part of the first conversion layer adjacent to the firstelectrode has an energy gap lower than that of a part of the firstconversion layer adjacent to the second electrode, wherein the firstconversion layer has a composition of M¹ _(m)M² _((1−m))AX¹ _((2m+t))X²_((3−2m−t)), 1≧m≧0, and 1≧t≧0, and the first conversion layer is acomposition-gradient perovskite obtained by gradually decreasing thepart by mole of m and t as the deposition proceeds; wherein each of M¹and M² is independently a divalent cation of Ge, Sn, or Pb, wherein A isa monovalent cation of methylammonium, ethylammonium, or formamidinium,wherein each of X¹ and X² is independently a monovalent anion ofhalogen, wherein M¹ has a lower atomic number than M², X¹ has a higheratomic number than X², or a combination thereof.
 2. The method asclaimed in claim 1, wherein the first deposition source, the seconddeposition source, and the third deposition source comprise a sputteringsource or an evaporation source.
 3. The method as claimed in claim 1,further comprising depositing a second conversion layer between thefirst conversion layer and the first electrode, wherein a part of thesecond conversion layer adjacent to the first electrode has an energygap higher than that of a part of the second conversion layer adjacentto the first conversion layer, a part of the second conversion layeradjacent to the first conversion layer has an energy gap equal to thatof a part of the first conversion layer adjacent to the secondconversion layer, and a part of the second conversion layer adjacent tothe first electrode has an energy gap lower than that of a part of thefirst conversion layer adjacent to the second electrode, wherein thestep of depositing the second conversion layer comprises: providing m′parts by mole of M³X³ ₂ by a fourth deposition source, providing 1−m′parts by mole of M⁴X⁴ ₂ by a fifth deposition source, and providing anamount of AX³ _(t′)X⁴ _((1−t′)) by a sixth deposition source to depositthe second conversion layer on the first electrode, wherein the secondconversion layer has a composition of M³ _(m′)M⁴ _((1−m′))AX³_((2m′+t′))X⁴ _((3−2m′−t′)), 1≧m′≧0, and 1≧t′≧0, and the secondconversion layer is a composition-gradient perovskite obtained bygradually decreasing the part by mole of m′ and t′ as the depositionproceeds; wherein each of M³ and M⁴ is independently a divalent cationof Ge, Sn, or Pb, wherein A is a monovalent cation of methylammonium,ethylammonium, or formamidinium, wherein each of X³ and X⁴ isindependently a monovalent anion of halogen, wherein M³ has a higheratomic number than M⁴, X³ has a lower atomic number than X⁴, or acombination thereof.
 4. The method as claimed in claim 3, wherein thefourth deposition source, the fifth deposition source, and the sixthdeposition source comprise a sputtering source or an evaporation source.5. A method of manufacturing a solar cell, comprising: providing m partsby mole of M¹X¹ ₂ by a first deposition source and providing 1−m partsby mole of M²X² ₂ by a second deposition source to deposit a M¹ _(m)M²_((1−m))X¹ _(2m)X² _((2−2m)) layer on a first electrode; providing AX¹or AX² by a third deposition source, such that AX¹ or AX² reacts withthe M¹ _(m)M² _((1−m))X¹ _(2m)X² _((2−2m)) layer to form a firstconversion layer on the first electrode, wherein the first conversionlayer is a composition-gradient perovskite of M¹ _(m)M² _((1−m))AX¹_((2m+1))X² _((2−2m)) or M¹ _(m)M² _((1−m))AX¹ _((2m))X² _((3−2m))obtained by gradually decreasing the part by mole of m as the depositionproceeds; and forming a second electrode on the first conversion layer,wherein a part of the first conversion layer adjacent to the firstelectrode has an energy gap lower than that of a part of the firstconversion layer adjacent to the second electrode, wherein 1≧m≧0;wherein each of M¹ and M² is independently a divalent cation of Ge, Sn,or Pb, wherein A is a monovalent cation of methylammonium,ethylammonium, or formamidinium, wherein each of X¹ and X² isindependently a monovalent anion of halogen, wherein M¹ has a loweratomic number than M², X¹ has a higher atomic number than X², or acombination thereof.
 6. The method as claimed in claim 5, wherein thefirst deposition source, the second deposition source, and the thirddeposition source comprise a sputtering source or an evaporation source.7. The method as claimed in claim 5, further comprising depositing asecond conversion layer between the first conversion layer and the firstelectrode, wherein the second conversion layer is a composition-gradientperovskite, a part of the second conversion layer adjacent to the firstelectrode has an energy gap higher than that of a part of the secondconversion layer adjacent to the first conversion layer, a part of thesecond conversion layer adjacent to the first conversion layer has anenergy gap equal to that of a part of the first conversion layeradjacent to the second conversion layer, and a part of the secondconversion layer adjacent to the first electrode has an energy gap lowerthan that of a part of the first conversion layer adjacent to the secondelectrode, wherein the step of depositing the second conversion layercomprises: providing m′ parts by mole of M³X³ ₂ by a fourth depositionsource and providing 1−m′ parts by mole of M⁴X⁴ ₂ by a fifth depositionsource to deposit a M³ _(m′)M⁴ _((1−m′))X³ _(2m′)X⁴ _((2−2m′)) layer onthe first electrode; and providing AX³ or AX⁴ by a sixth depositionsource, such that AX³ or AX⁴ reacts with the M³ _(m′)M⁴ _((1−m′))X³_(2m′)X⁴ _((2−2m′)) layer to form a second conversion layer on the firstelectrode, wherein the second conversion layer is a composition-gradientperovskite of M³ _(m′)M⁴ _((1−m′))AX³ _((2m′+1))X⁴ _((2−2m′)) or M³_(m′)M⁴ _((1−m′))AX³ _((2m′))X⁴ _((3−2m′)) obtained by graduallydecreasing the part by mole of m′ as the deposition proceeds; wherein1≧m′≧0; wherein each of M³ and M⁴ is independently a divalent cation ofGe, Sn, or Pb, wherein A is a monovalent cation of methylammonium,ethylammonium, or formamidinium, wherein each of X³ and X⁴ isindependently a monovalent anion of halogen, wherein M³ has a higheratomic number than M⁴, X³ has a lower atomic number than X⁴, or acombination thereof.
 8. The method as claimed in claim 7, wherein thefourth deposition source, the fifth deposition source, and the sixthdeposition source comprise a sputtering source or an evaporation source.